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Combustion and Emission Characteristics of WDF in a Light-Duty Diesel Engine over Wide Load Range 2017-01-2265

Wide Distillation Fuel (WDF) refers to the fuels with a distillation range from initial boiling point of gasoline to final boiling point of diesel. Recent experimental results have shown WDF by blending 50% gasoline and 50% diesel (G50) exhibits much lower soot emissions than diesel at medium load with similar thermal efficiency. However, the engine performances fueled by G50 at both low load end and high load end are still unknown. In this study, the combustion and emission characteristics of G50 and diesel are compared over a wide load range from 0.2 MPa IMEP to 1.4 MPa IMEP at a light-duty diesel engine. The results shown that at 0.2 MPa IMEP, G50 exhibits low combustion stability and thermal efficiency. With the increase of load, the poor combustion quality of G50 is improved. G50 can achieve soot-free combustion up to 1.0 MPa IMEP, while diesel cannot. At 1.4 MPa IMEP, the difference of CA50 and ignition delay between diesel and G50 is diminished especially for early SOI conditions, however, G50 still exhibits larger premixed heat release ratio, more rapid premixed-combustion heat release and much lower soot emissions compared with diesel. A three-dimensional engine combustion simulation is conducted by using SAGE combustion model coupled with a reduced primary reference fuel reaction mechanism. By analyzing the simulation results, it’s found that large ratio of lean mixture existing in squish volume is the reason for the inferior combustion quality of G50 at low load. The reason for low soot emissions of G50 at high load are the lower equivalence ratio downstream the spray due to the high volatility and injection ending before ignition which decreases ratio of diffusion combustion.